Atopic disorders, such as asthma, allergic rhinitis and atopic dermatitis, are known to be associated with higher than normal rates of depression and anxiety. Likewise, several behavioral disorders, including depression, panic disorder and social anxiety, have been linked with high rates of atopic signs and symptoms. It is unclear whether this covariation of atopy with behavioral disorders is due to effects of one disorder causing the other, or to either an environmental or genetic common risk factor. One methodology useful for ascertaining the proportion of variance of a phenotype due to genetic or environmental effects is the twin study design. This study proposes to more fully determine the proportion of covariance due to common genetic or environmental factors underlying atopy and behavioral symptoms by use of detailed laboratory measurements of atopy, as well as several self report measures of depression, anxiety, personality factors and health care behaviors, in monozygotic (MZ) and dizygotic (DZ) adolescent twins. The Specific aims of the study are: 1) To establish the covariance of atopy and affective and anxiety symptoms in MZ and DZ twin pairs; 2) To determine what proportion of the co-variance is due to genetic (A), shared (C) or non-shared environmental (E) factors; 3) To establish the portion of variance in health care behaviors due to genetic (A), shared (C) or non-shared environmental (E) inputs; and 4) To establish the covariance of depression, anxiety and health behaviors in monozygotic (MZ) and dizygotic (DZ) twin pairs.